Lagenidium giganteum (Oomycetes: Lagenidiales) is currently the most promising microbial agent for biological control of mosquito larvae. With increasing resistance of many mosquitoes to insecticides a well documented phenomenon, the availability of technically and commercially viable alternatives is obvious. The ultimate objective of the proposed research is to improve fermentation production of the sexual oospore stage of the fungus, and to sufficiently increase control of oospore germination by developing suitable maturation and formulation protocols, that L. giganteum can be economically produced on a large scale for field control of mosquitoes. Chemical and physical factors not known to affect fermentation production of oospores will be systematically modified to improve yields. Oospore yields will be related to the structure, concentration and cellular distribution of sterols and fatty acids, which have profound effects on oosporogenesis. Factors regulating oospore maturation and germination will be identified in the laboratory using direct microscopic observation and indirectly monitored using sentinel mosquitoes. This information will be used to develop oospore formulations for specific mosquito species, e.g. synchronously germinating spores for control of floodwater species and asynchronous preparations for control of multivoltine species under field conditions. It is anticipated that these investigations will lead to commercial production of L. giganteum oospores for mosquito control.